Infrared thermal imaging method has started to be used in routine controls due to the disadvantages (uses ionizing energy, applies pressure) of mammography, which is frequently used in the diagnosis of breast cancer. With passive thermography, infrared radiation emitted naturally from the body surface is detected by a thermal camera and the surface temperature distribution is displayed. Using a passive thermal imaging system with 30 mK thermal sensitivity, 10 mm tumor can be detected at a depth of 12 mm. The performance of passive thermography is limited for small and deep tumors. In the active thermography method, it is aimed to detect deeper tumors by using an external heat source. In the active thermography method, deeper tumors are detected using external heat sources. In this study, the currents induced by time varying magnetic fields (27.12 MHz) were used as the external heat source. In the simulation study, breast and cancerous tissue were modeled in three dimensions and the bioheat equation for active and passive modes was solved by using realistic values of the tissues. As a result of the simulation studies, it was observed that a 10 mm malignant tumor could be detected up to a depth of 20 mm. It was shown that this method can be used with multiple frequencies as the temperature distributions obtained from the surface for different frequency values are different from each other.